Submerged combustion method, which is also referred to as in-liquid combustion method, is a new type of combustion technology. Fuel and air are fully mixed and fed into combustion chamber for complete combustion, and the generated high temperature gas is expelled into liquid directly to heat up the liquid. The combustion process of submerged combustion method implements a heat transfer process that is a direct-contact heat transfer process.
As a high efficiency heat transfer method, submerged combustion method has been used in such industries as chemical industry, etc. Due to the fact of its high heat transfer efficiency comparing to other heat transfer methods, both domestic and international thermal energy industries started to focus on applying this method in small size boilers, in order to improve heat energy consumption efficiency and saving fuel.
For the existing submerged combustion boilers, an additional blower is needed for blowing air into the combustion chamber in order to mix with fuel and combust. Then the high temperature gas will be expelled against water pressure into water for heat exchange. Due to the fact that the additional blower must meet the requirements for high pressure and large air flow, considerable extra energy has to be consumed, which will comprise the high efficiency associated with the submerged combustion method. American U.S. Pat. No. 5,735,235 “METHOD AND SYSTEM FOR HEATING A LIQUID” has provided a submerged combustion method and system, which has applied the energy saving principle of “Using combustion heat energy directly to suck in the required air for combustion”. But because it used a piston type engine burner and a direct-jet heat exchange method, the invention disclosed in this patent has the disadvantages of high mechanical energy consumption, limited exhausting pressure, low air utilizing rate, etc. So, its systematic energy utilization rate can still be improved.